A galvanostat is used to control the current flowing through an electrochemical cell. A schematic diagram of a constant-current galvanostat is shown here where A is the auxiliary electrode, W is the working electrode, R is an optional reference electrode, E is a high-impedance potentiometer, and i is an ammeter.
The current flowing from the power supply through the working electrode is
i = EPS/(R + Rcell)
where EPS is the potential of the power supply, R is the resistance of the resistor, and Rcell is the resistance of the electrochemical cell. If R >> Rcell, then the current between the auxiliary and working electrodes
i ≈ EPS/R
essentially is constant. To monitor the potential of the working electrode, which changes as the composition of the electrochemical cell changes, we can include an optional reference electrode and a high-impedance potentiometer.
